The present invention relates to the field of optical processing, and more particularly to optical coherent processors.
Optical processors or correlators have been used for years in many different applications among which are target tracking, quality control and pattern recognition. In a typical optical correlator, a coherent source such as a laser generates a light beam that is collimated to illuminate an input imaging object or device as part of the correlator for generating an input image to be processed. The correlator comprises a first lens used to perform a first Fourier transform of the input image, which transform appears in the Fourier or filter plane. As well known by one skilled in the art, when applied to optical processing, the Fourier transform is a complex (real and imaginary parts) function resulting to an optical pattern lying in the spatial frequency domain. The correlator further comprises a second imaging device positioned within the Fourier plane to display a selected filter. At the filter plane, the Fourier transform of the input image is multiplied by the transmission function displayed on the filter device, to produce a combined image. Typically, the characteristics of the filter can be adapted either to perform pattern recognition, wherein the filter characteristics are based on the Fourier transform of a reference object to be recognized, or to perform filtering or other processing operations based on a predetermined mathematical function. The correlator further comprises a second lens for performing the inverse-Fourier transform of the combined image, resulting to a correlated, convoluted or filtered image, depending of the particular processing or filter function used. Known optical correlators or processors commonly use a spatial light modulator as the second imaging device, which modulator is conveniently computer-controlled using a specific software implementing a plurality of processing or filter functions that can be selected by one or more users. Especially in the case where the use of an optical correlator or processor should be limited to a reduced number of persons within an organization, it is desirable to provide particular means for limiting system access to authorized persons only. Furthermore, each individual user might require that information specific to his work, e.g. operation parameters, specific processing functions, as stored in the computer memory of the system could not be accessed by unauthorized users.
Phase masks have been used for long time mainly in the domain of kinoforms as described by L. B. Lesem et al. in xe2x80x9cThe kinoform, a new wavefront reconstruction devicexe2x80x9d, IBM J. Res. Develop, vol. 13, p. 150, 1969, and by A. Tanone et al. in xe2x80x9cPhase modulation depth for a real-time kinoform using a liquid crystal televisionxe2x80x9d, Optical Engineering, vol. 32, no. 3, p. 517, 1993. In the design of kinoforms, phase masks have been used to generate pattern diffraction so that, when illuminated by coherent light, the encoded pattern is observed in the far-field of propagation.
More recently, phase masks have been applied to optical image encryption and decryption of information encoded on an object or to authenticate the object in itself. In a typical phase encryption/decryption application, a phase key is incorporated in an input external object presented to a correlator which comprises a fixed key. The use of phase masks for various security purposes is abundantly referred to in the literature. In U.S. Pat. No. 5,485,312 issued on Jan. 16, 1996 to Horner et al., there is disclosed an optical pattern recognition system and method for verifying the authenticity of an object, which employ a joint transform coherent optical processor. An unreadable and hence counterfeit-proof encrypted phase mask is coupled to the object and the optical processor compares the phase mask with a reference phase mask having the same phase code thereon. The processor produces a correlation spot having an intensity that exceeds a given level if the phase mask is genuine. In xe2x80x9cOptical pattern recognition for validation and security identificationxe2x80x9d, Optical Engineering, vol. 33, no. 6, 1994, p. 1752, and in xe2x80x9cFully phase encoded key and biometrics for security versificationxe2x80x9d Optical Engineering, vol. 36, no. 3, p. 935, 1997, B. Javidi et al. teach encryption and decryption techniques for authenticating an object with a phase mask in a spatial plane, external to a correlator, without discussing alignment and/or rotation problems that are likely to occur with such techniques. In xe2x80x9cOptical image encryption based on input plane and Fourier plane random encodingxe2x80x9d, Optics Letters, vol. 20, no. 7, p. 767, P. Refregier and al. teach the use of a two-phase mask for carrying out image encryption and decryption, without consideration of alignment and speckle noise problems that are likely to be observed. In xe2x80x9cIncoherent optical correlators and phase encoding of identification codes for access control of authenticationxe2x80x9d Optical Engineering, Vol. 36, no. 9, p. 2409 1997, J. Brashner et al. propose the use of incoherent processors for encryption and decryption, for the purpose of authenticating separate objects. In xe2x80x9cDistributed kinoforms in optical security applicationsxe2x80x9d Optical Engineering, vol. 35, no. 9, p. 2453, 1996, P. Stepien and al. teach decryption and encryption of information techniques that are based on computer generated holograms. In xe2x80x9cOptical implementation of image encryption using random phase encodingxe2x80x9d, Optical Engineering, vol. 35, no. 9, p. 2459. 1996, G. Neto et al. propose a correlator architecture for encryption and decryption, where speckle noise problems are taken into consideration. In xe2x80x9cRandom phase encoding for optical securityxe2x80x9d, Optical Engineering, vol. 35, no. 9, p. 2464, 1996, R. K. Wang teaches encryption and decryption techniques also using an optical correlator, without considering alignment and/or rotation problems that are inherent to such techniques. In xe2x80x9cPractical image encryption scheme by real-valued data, Optical Engineeringxe2x80x9d, vol. 35, no. 9, p. 2473, 1996, H.-G. Yang et al. describe encryption and decryption schemes that are based on amplitude reference mask and object. In xe2x80x9cExperimental demonstration of the random phase encoding technique for image encryptionxe2x80x9d, Optical Engineering, vol. 35, no. 9, p. 2506, 1996, Javidi et al. report experimental results of encryption and decryption performed with techniques using an optical correlator, wherein bending, noise, and scratches problems were observed with these techniques.
It is therefore a main object of the present invention to provide image processing apparatus and method with a locking feature, for limiting access thereof to authorized persons only.
It is a further object of the present invention to provide image processing apparatus and method with locking feature ensuring that processing information specific to a user could not be accessed by unauthorized users.
It is a still further object of the present invention to provide a lock device for controlling the use of an optical image processor.
It is another object of the present invention to provide image processing apparatus and method as well as lock device and method for controlling the use of an optical image processor, which make use of an optical mask implementing a locking mask function and without including any movable part, thereby obviating problems of alignment in position/rotation, bending, scratches, space bandwidth, or speckle inherent to the use of an external object as taught in the prior art.
The present invention can be generally defined as an optical key for preventing unauthorized use of an optical coherent processor and more precisely of an optical correlator. The principle underlying this invention uses an optical lock in combination with an encoded software key superimposed on a filter image. The optical lock, preferably in hardware form, consists of a first optical mask implementing a locking mask function that is preferably complex (phase and/or amplitude) which first optical mask is included in the optical path of the correlator. The mask is fixed during assembly of the correlator and a unique pattern is encoded thereon. The software key consists of a pattern defined by a key mask function that is displayed preferably using a spatial light modulator as part of a second optical mask included on the correlator optical path. The key mask function is designed to compensate for the wave-front distortion generated by the locking mask function of the first optical mask. Therefore, a correlator provided with its unique hardware lock cannot generate useful correlation, unless a corresponding unique software key is used.
According to the above mentioned objects, from a broad aspect of the present invention, there is provided an apparatus for processing an input image produced by an imaging device illuminated by a coherent light source. The apparatus comprises first Fourier transform means for performing the Fourier transform of the input image to generate a corresponding transformed input image in the spatial frequency domain within an area defined by a Fourier transform filter plane, and first optical mask means being disposed within said area, said first optical mask implementing a locking mask function. The apparatus further comprises data processor means for generating filter mask function control data, second optical mask means disposed within said area, said second optical mask means implementing a filter mask function according to the filter mask function control data to generate with the locking mask function a combined image in the spatial frequency domain, and second Fourier transform means for performing the inverse Fourier transform of the combined image to generate a processed image only if the filter mask function control data include key control data corresponding to a key mask function complementary to the locking mask function for substantially cancel the locking effect thereof.
From another broad aspect of the invention, there is provided a lockable coherent optical processing apparatus comprising a laser source for generating substantially coherent light, an input imaging device receiving the coherent light to produce an input image, first Fourier transform means for performing the Fourier transform of the input image to generate a corresponding transformed input image in the spatial frequency domain within an area defined by a Fourier transform filter plane, and first optical mask means being disposed within said area, said first optical mask implementing a locking mask function. The apparatus further comprises data processor means for generating filter mask function control data, second optical mask means disposed within said area, said second optical mask means implementing a filter mask function according to the filter mask function control data to generate with the locking mask function a combined image in the spatial frequency domain, and second Fourier transform means for performing the inverse Fourier transform of the combined image to generate a processed image only if the filter mask function control data include key control data corresponding to a key mask function complementary to the locking mask function for substantially cancel the locking effect thereof.
From still another broad aspect of the invention, there is provided an optical correlator for analyzing an input image produced by an imaging device illuminated by a coherent light source. The optical correlator comprises first Fourier transform means for performing the Fourier transform of the input image to generate a corresponding transformed input image in the spatial frequency domain within an area defined by a Fourier transform filter plane and first optical mask means being disposed within said area, said first optical mask implementing a locking mask function. The correlator further comprises data processor means for generating filter mask function control data, second optical mask means disposed within said area, said second optical mask means implementing the filter mask function according to the filter mask function control data to generate with the locking mask function a combined image in the spatial frequency domain, and second Fourier transform means for performing the inverse Fourier transform of the combined image to generate a correlation indicating image only if the filter mask function control data include key control data corresponding to a key mask function complementary to the locking mask function for substantially cancel the locking effect thereof.
From a further broad aspect of the invention, there is provided a lock device for controlling the use of an optical image processor including a laser source for generating and directing substantially coherent light onto an input imaging device producing an input image, first Fourier transform means for performing the Fourier transform of the input image to generate a corresponding transformed input image in the spatial frequency domain within an area defined by a Fourier transform filter plane, second Fourier transform means for performing the inverse Fourier transform of the transformed input image to be combined in the spatial domain with a filter mask image to generate a processed image. The lock device comprises first optical mask means being disposed within said area, said first optical mask implementing a locking mask function, data processor means for generating filter mask function control data and second optical mask means disposed within said area, said second optical mask means implementing a filter mask function according to the filter mask function control data to generate with the locking mask function the filter mask image, wherein the processed image is generated by the image processor only if the filter mask function control data include key control data corresponding to a key mask function complementary to the locking mask function for substantially cancel the locking effect thereof.
From a still further broad aspect of the invention, there is provided a method of processing an input image produced by an imaging device illuminated by a coherent light source. The method comprises the steps of a) performing the Fourier transform of the input image to generate a corresponding transformed input image in the spatial frequency domain within an area defined by a Fourier transform filter plane; b) combining the transformed input image with a filter mask image and a locking mask image respectively defined by a filter mask function and a locking mask function to generate a combined image in the spatial frequency domain; and c) performing the inverse Fourier transform of the combined image to generate a processed image only if the filter mask function include a key mask function complementary to the locking mask function for substantially cancel the locking effect thereof.